The invention relates to the field of sinterable and/or fusible ceramic masses, hereinafter termed ceramic masses, and shaped articles comprising ceramic masses, in particular in the field of bioactive or bioreactive bone replacements, i.e. a ceramic mass which acts to produce a direct bone contact free of connective tissue, with long-term stability, and a production and construction process therefor.
The term “ceramic mass” as used in this connection should be understood to mean an inorganic non-metallic substance, both in sintered, fired form, as well as in the form of a prepared material for sintering or firing. A ceramic shaped article is typically moulded from a raw mass at room temperature, for example a slip or a paste, and solidified by a high temperature sintering process. The preparation of a material for sintering may also include a first sintering step and subsequent grinding of the sintered material, for example, so that the ground material is then reused for the production of a slip or a paste from which a green body is formed. The green body can result in a sintered glass-ceramic, for example. This preparation may also include grinding previously fused glass. Further, it is possible for the molten glass to undergo a heat treatment so that—in accordance with conventional glass-ceramic processes—a crystallization occurs in the glass matrix.
The ceramic mass may be either a granulate which is used directly after appropriate pre-treatment to replace natural bone material or to supplement a bone in a living organism. Likewise, however, the ceramic mass may be processed to form a shaped article which, after suitable pre-treatment, completely replaces a bone in a living organism. Applicable processing procedures also additionally include additive manufacturing processes, for example what is known as 3D printing and other rapid prototyping processes, and optional subsequent separate sintering steps or even impregnation or colonization of the structures obtained with living cells.
Known bioactive/bioreactive glass-ceramics or ceramic masses with long-term stability predominantly consist of apatite and wollastonite. They can be prepared as sintered glass-ceramic (Kokubo [1]) or by traditional glass-ceramic processes (Berger et al [2]). Pure hydroxyapatite materials, which a priori are considered to be bioactive and have long-term stability, cannot be produced by any manner, especially as printed shaped articles, and are generally not strong enough to be used as a bone substitute material. In this context, a “bone substitute with long-term stability” or a “composite with long-term stability”, as opposed to a resorbable material or a resorbable material composite, should be understood to mean a material which is not resorbed and not replaced by natural bone, but is substantially preserved during the service period which, for example, corresponds to the typical lifetime of the respective organism (vertebrate, man). Its solubility in the living organism or under physiological conditions of a cell and/or tissue culture is thus extremely low. This is shown by the fact that over the entire service period an interfacial surface of the material on which natural bone can accumulate is preserved in the organism in a continuous remodelling process, or the interfacial surface has an abrasive action in a technical application.
In particular, the solubility of known products based on glass-ceramics which exclusively contain the major crystalline phases apatite and wollastonite is still too high. If the solubility is reduced by the addition of Al2O3, ZrO2 or TiO2, then the resistance of the material under physiological conditions or in physiological solution is increased as a function of the quantity of additive, but this decreases the rate of formation of connective tissue-free direct bone contact because these substances (Al2O3, ZrO2, TiO2) are deposited and separate layers are formed [3].